Effect of the Heating Rate on the Spark-Plasma-Sintering (SPS) of Transparent Y2O3 Ceramics: Microstructural Evolution, Mechanical and Optical Properties

High strength transparent Y2O3 ceramics were fabricated from commercial powders using spark plasma sintering (SPS) technique by optimizing the heating rate. The heating rate significantly influenced the microstructures and the optical/mechanical properties of the Y2O3 ceramics. Grain growth was limited accordingly with increasing the heating rate. The ball milling process of the commercial Y2O3 powders is likely to further enhance the sinterability during the SPS processing. The dense Y2O3 ceramics, which were sintered by SPS with 100 degrees C/min, showed good transmittance range from visible to near infrared (IR). For a high heating rate of 100 degrees C/min, the in-line transmittance at a visible wavelength of 700 nm was 66%, whereas for a slow heating rate of 10 degrees C/min, it reduced to 46%. The hardness H-v tends to increase with increasing the heating rate and rigorously followed the Hall-Petch relationship; that is, it is enhanced with a reduction of the grain size. The toughness K-IC, on the other hand, is less sensitive to both the heating rate and the grain size, and takes a similar value. This research highlighted that the high heating rate SPS processing can fabricate fully dense fine-grained Y2O3 ceramics with the excellent optical and mechanical properties.